1. Field of the Invention
This invention relates generally to electric vehicle battery pack thermal management and, more particularly, to a method and system for managing the temperature in an electric vehicle battery pack which allows a battery pack at a high state of charge and/or high remaining useful life to be operated at a lower temperature than a battery pack at a lower state of charge and/or lower remaining useful life, thus reducing energy expenditure on battery pack heating and maximizing vehicle driving range, while still optimizing battery pack performance and durability.
2. Discussion of the Related Art
Electric vehicles are rapidly gaining popularity in today's automotive marketplace. Electric vehicles offer several desirable features, such as eliminating local emissions and usage of petroleum-based fuels at the consumer level, and potentially lower operating costs. A key component of electric vehicles is the battery pack, which can represent a substantial proportion of the vehicle's cost. Battery packs in these vehicles typically consist of numerous interconnected cells, which are able to deliver a lot of power on demand. Maximizing battery pack performance and life are key considerations in the design and operation of electric vehicles.
In order to maximize battery pack performance and durability, the temperature in the battery pack must be maintained at a certain minimum level when the battery pack is discharging during vehicle operation. Control systems in existing electric vehicles typically prescribe a constant minimum temperature in the battery pack, irrespective of state of charge or remaining useful life of the battery pack, and use an onboard thermal management system to ensure battery pack temperature is at or above the minimum set point level during vehicle operation. However, using the thermal management system to warm the battery pack before or during driving operation consumes energy, which detracts from the driving range of the vehicle. It has now been observed that the performance of lithium-ion battery packs can still be sufficient to meet vehicle requirements if the minimum set point temperature in the battery pack is lowered for battery packs with a high state of charge and/or remaining useful life. In addition, lowering the temperature set point is beneficial for battery durability.
There is an opportunity to employ a battery pack thermal management methodology which determines minimum set point temperature as a function of state of charge and remaining useful life, thus ensuring optimum battery pack performance and life, but also maximizing vehicle range by not expending energy to warm the battery pack unnecessarily. Such a method could increase customer satisfaction through improved vehicle driving range and decreased power consumption from the grid.